This invention relates to a rubber or plastics-coated roller, such as a fixing roller to be used in the thermal fixing part of an electrophotographic copying machine, and to a method for production thereof and an apparatus for carrying out the method.
The rubber or plastics-coated rollers heretofore used in the thermal fixing part of electrophotographic copying machines have been formed, as illustrated in Fig. 6, of a core shaft 1 consisting of a main core shaft member 1a and a support part 1 b and a rubber or plastics layer 2 formed on the periphery of the main core shaft member 1a. Such rollers are produced by the following method as described in Japanese Patent Publication SHO 55(1980)-30967). With reference to the diagram, a bottom member 4 having a blind hole 4a formed at the centre on the upper side thereof is fitted into the lower part of a cylindrical mold 3 and a prescribed amount of liquid rubber or plastics is poured into the cylindrical mold 3. Then a core shaft 1 is inserted into the cylindrical mold 3, the support part 1b of the core shaft 1 is fitted in the blind hole 4a, and the core shaft 1 is fixed in position by fitting, into the upper part of the cylindrical mold 3, a retainer lid 5 provided at the centre thereof with a support hole 5a adapted to support shaft 1.
In the resulting configuration, the liquid rubber or plastics is left standing for a while until the rubber or plastics material is set. Subsequently, the core shaft 1 is drawn out of the cylindrical mold 3 to produce a rubber or plastics-coated roller.
However, when the production of the rubber or plastics-coated roller is carried out by the method described above, the core shaft, during its insertion, is liable to entrain air into the rubber or plastics material. The entrapped air may survive, as the rubber or plastics material gains in viscosity with the advance of its setting, in the form of bubbles in the coating layer and causes serious degradation of the rubber quality. The retainer 5 is provided with an air vent (not shown). The rubber or plastics material, when cured, gives rise to burrs in the part corresponding to the air vent so that the produced rubber or plastics-coated roller requires extra work for finishing the edge.
Recently, a method for producing a rubber or plastics-coated roller by using an apparatus constructed as illustrated in Fig. 7 has been proposed (Japanese Patent Publication SHO 59(1984)-371). This method effects the production of the rubber or plastics-coated roller by providing a container 7 with a movable bottom plate 26 provided with a sealing 2a, connecting a receiving base 10 to an upper lid 9 of the container 7, setting a core shaft 11 and a cylindrical case 12 at prescribed positions on the receiving base 10, pressing and fixing them in position with a retainer cap 13 disposed on the case provided with an air vent part 13a, and gradually pushing upwardly the bottom plate 26 thereby causing the rubber or plastics material 8 to be pressed into a cavity 15 via an opening part 14 and a conduit 14a. When the bottom plate 26 held in the state illustrated is pushed upwardly, a check valve 16 is actuated as the inner pressure of the cavity 15 inside the case 12 and the pressure for pushing up the bottom plate 26 are equilibrated. The rubber or plastics-coated roller is obtained under conditions such that the inner pressure of the cavity 15 is retained until the rubber or plastics material is set.
In the apparatus constructed as described above, however, the removal of set material from the opening part, the check valve, and the conduit is extremely difficult. This construction has another disadvantage that the set material forms burrs in the part corresponding to the air vent, causes air bubbles which are not good for the product near the end faces of the rubber or plastics-coated layer, and increases the waste products.
Further, the conventional roller producing apparatus suffers from yet another disadvantage in that during the introduction of liquid rubber or plastics material for replenishment into the container, the upper lid 9 fitted to the upper part of the container 7 must be removed and this removal of the upper lid lowers the efficiency of operation.
The present invention seeks to overcome the conventional drawbacks mentioned above. It aims to provide a method for the production of a rubber or plastics-coated roller, which curbs entrapping air into the rubber or plastics layer, substantially obviates the necessity for such secondary treatment as polishing, which is otherwise required after the setting of the liquid rubber or plastics, permits manufacture of rollers of high dimensional accuracy, and enables the apparatus to be prepared by simple cleaning for subsequent cycles.
According to one aspect of this invention we provide a rubber or plastics-coated roller, comprising a core shaft having support parts at each opposite end of a main core shaft member which roller is characterised by interconnecting tapered surfaces provided in an end side of said main core shaft member and in an end side of a rubber or plastics layer formed on the main core shaft member.
A method for the production of a rubber or plastics-coated roller according to the present invention comprises providing a cylindrical mold held upright, an upper plug and a lower plug disposable in upper and lower parts of said cyindrical mold and a core shaft intended for placement in said cylindrical mold, which method is characterised by the steps of fitting into the lower part of said cylindrical mold said lower plug provided in the inside thereof with a tapered surface for guiding said core shaft and, at the centre thereof, with a material injection hole, inserting into said cylindrical mold said core shaft having tapered surfaces each one formed at the opposite ends thereof and optionally having caps fitted on each one of said opposite ends, fitting into the upper part of said cylindrical mold said upper plug provided in the inside thereof with a tapered surface for guiding said core shaft and, at the centre thereof, with an air vent, injecting rubber or plastics liquid into said cylindrical mold through said material injection hole in said lower plug and allowing said rubber or plastics liquid to set.
Apparatus for the production of a rubber or plastics-coated roller according to the present invention comprises a production die, preferably a metal die, which die comprises a cylindrical mold held upright, an upper plug and a lower plug disposed in the upper and lower parts of said cylindrical mold, a core shaft placed in said cylindrical mold and a rubber or plastics injection device, which apparatus is characterised in that said lower plug is provided in the inside thereof with a tapered surface for guiding said core shaft and, at the centre thereof, with a material injection hole, said core shaft has at opposite ends thereof tapered surfaces optionally each covered with a cap possessing a tapered surface, said upper plug is provided in the inside thereof with a tapered surface for guiding said core shaft and, at the centre thereof, with an air vent and fitted into the upper part of said cylindrical mold, and said rubber or plastics injection device is connected to said lower plug.
The invention will now be described by way of example with reference to the accompanying drawings, wherein:
Fig. 1 is a longitudinal cross section schematically illustrating a typical embodiment of a method and apparatus for the production contemplated by this invention. This apparatus is furnished with a cylindrical mold 30 possessing an inside diameter equalling the diameter of a roller being molded and a lower plug 40 detachably fitted into the lower part of the cylindrical mold 30, and an upper plug 70 slidably fitted to the upper part of the cyindrical mold 30. In the inside end face of the lower plug 40, is disposed a tapered surface 41 contacted with a tapered surface 19 of a core shaft 1 a, and a material injection hole 42 is disposed in a shaft centre of the lower plug 40.
The inside end face of the upper plug 70 incorporates therein a tapered surface 71 for guiding the core shaft. Protruding portions 40a and 70a are disposed in the side of the lower plug 40 and the upper plug 70 respectively. There is also provided an elastic member 22 such as a rubber ring or a coil spring having one end thereof hung on the upper plug 70 and the other end on the lower plug 40 respectively.
The apparatus is further provided with a rubber or plastics material injection mechanism 23 communicating with the central hole 42 of the lower plug 40. This rubber or plastics material injection mechanism 23 is a cylindrical container 25 which is provided with a piston 24 and contains therein the rubber or plastics material 8 treated in advance for the purposes of deaeration under a vacuum. Actual examples of the rubber or plastics material for the roller molding include silicone rubber, thiokol rubber, chloroprene rubber, butadiene rubber, polyurethane rubber, elastic epoxy resin, styrene butadiene block copolymer, thermoplastic polyurethane, polyether-polyester block polymer, trans- and 4-polyisoprene, thermoplastic polyolefin, butyl-, craft-, and ethylene-based thermoplastic elastomers, and even methyl methacrylate, 6-nylon, and general purpose epoxy resin.
The method for the production of a rubber or plastics-coated roller by the use of the apparatus of the present invention will now be described.
The core shaft 1 is inserted into the cylindrical mold 30 and the upper plug 70 and the lower plug 40 are fitted into the opposite ends respectively.
Then, one end of the ring type elastic member 22 is hung on a protruding portion 70a of the upper plug 70 and the other end thereof on a protruding portion 40a of the lower plug 40, so as to keep both members urged toward each other at all times.
In the condition consequently assumed, the tapered surface 19 of the core shaft and the lower plug 40 are held fast against each other. Then, the lower plug 40 and the container 25 are interconnected and the piston 24 of the rubber or plastics material injection mechanism 23 is elevated. As a result, the flow pressure of the rubber or plastics material 8 gives an upward push to the core shaft 1 and interposes a gap between the tapered end face 19 of the core shaft and the end face 41 of the lower plug 40, to admit the rubber or plastics material 8 into the empty space 21 of the mold. In consequence of this injection of the rubber or plastics material, the air entrapped inside the empty space 21 departs from the space formed between upper plug 70 and the end face of the core shaft 1 while giving a downward push to the upper plug 70. When the empty space 21 is filled with the material 8 and the inner pressure of this empty space 21 and the pressure P1 of the upward push are equilibrated, the core shaft 1 and the upper plug 70 descend and the end face 19 of the roller core shaft and the lower plug 40 jointly function as a check valve, with the result that the pressure in the empty space 21 will be kept intact until the rubber or plastics material is set.
Thus, the production of a rubber or plastics-coated roller by the apparatus of this invention is accomplished. The rubber or plastics layer of the roller so produced is not found to contain therein any discernible pinholes or bubbles. Burrs are partly formed on the end faces of the roller core shaft. Since these burrs are easily ripped off, the end faces of the roller do not require any special secondary fabrication. Further, the apparatus of the present invention is such that disposal of waste rubber, subsequent to the removal of the rubber roller from the mold, can be facilitated.
Because of the provision of the mechanism resembling a check valve, the possibility of liquid leakage during the transfer of the case is precluded and intermittent/continuous injection is made possible.
Fig. 2a is a longitudinal cross section illustrating part of a typical rubber or plastics-coated roller produced by the procedure of Example 1.
With reference to Figs. 2a to c, in a rubber or plastics-coated roller which is composed of a core shaft 1 consisting of a main core shaft member 1a a and support parts 1 b formed at the opposite ends of the main core shaft member 1 a and a rubber or plastics layer 2 is formed on the periphery of the shaft part, the end face 1c of the main core shaft member and the end face 2a of the rubber or plastics layer respectively possess tapered surfaces which extend into each other. Figs. 2a and 2b illustrate the two tapered surfaces having the same angle. Fig. 2c illustrates a tapered angle of the core shaft which is different from the angle of the tapered surface of the rubber or plastics layer.
By the structures as shown in Figs. 2a to 2c, the following effects can be obtained.
In the production of the roller, when the rubber or plastics material is injected into the cylindrical mold, the fluid resistance of the material decreases and prevents air entrapment. As a result, the formation of bubbles in the coating layer 2 is not likely to be caused. The shaft 1 is aligned automatically in the mold, so that obtained roller has a uniform wall-thickness. As a result, secondary treatment is not required.
Fig. 3 and Fig. 4 are cross sections illustrating another method and apparatus for the production of a rubber or plastics-coated roller as a further embodiment of the present invention. This embodiment comprises a cylindrical mold 30 possessing an inside diameter equalling the diameter of the roller being molded and held upright, a lower plug 40 fitted into the lower part of the cylindrical mold 30, provided in the inside thereof with a tapered surface 41 for guiding the core shaft, and having a material injection hole 42 opening at the centre thereof, a pair of caps 50 and 60 fitted to the opposite ends of a core shaft 1 inserted into the cylindrical mold 30 and possessing respectively tapered surfaces 51, 61 and an upper plug 70 fitted into the upper part of the cylindrical mold 30 and provided in the inside thereof with a tapered surface 71 for guiding the core shaft.
Grooves 72 for release of air are formed in the tapered surface 71 which is contacted with the cap 60 of the upper plug 70.
The material injection hole 42 in the lower plug 40 is joined to a material injection mechanism similar to the mechanism described in Example 1. The upper plug 70 is connected to an upper plug pressing mechanism which is not shown in the Figure.
As liquid rubber or plastics material 8 to be injected through the material injection hole 42 of the lower plug 40, silicone rubber, thiokol rubber, chloroprene rubber, or elastic epoxy resin can be used, for example.
Now, the method of this invention for producing the rubber or plastics-coated roller by the use of the apparatus constructed as described above will be explained below.
First, the cylindrical mold 30 is set upright, the lower plug 40 is fitted into the lower part of the cylindrical mold 30, and the cap 50 is inserted into the tapered surface 41 of the lower plug 40. Then, the core shaft 1 is inserted into the cylindrical mold 30, the supprt part 1 at one end is fitted into the cap 50, and the support part 1b at the other end is fitted into the cap 60.
Further, the upper plug 70 is fitted into the upper part of the cylindrical mold 30 and upper plug 70 is pressed with suitable pressure P1 to be exerted by the upper plug pressing mechanism. At this time the tapered surface 61 of the cap 60 comes into intimate engagement with the tapered surface 71 of the upper plug 70 and the tapered surface 51 of the cap 50 into engagement with the tapered surface 41 of teh lower plug 40.
Then, the injection mechanism is actuated to admit the liquid rubber or plastics material 8 through the material injection hole 42 of the lower plug 40 under pressure. At this time, the fluid pressure of the rubber or plastics material 8 gives an upward push to the core shaft 1 and the caps 50 and 60 at the opposite ends so as to admit the material 8 through the gap between the tapered surface 41 of the lower plug 40 and the tapered surface 51 of the cap 50 into the empty space intervening between the cylindrical mold 30 and the core shaft member 1a.
In the meantime, the tapered surface 61 of the cap 60 fitted on the upper part of the core shaft 1 is pressed against the tapered surface 71 of the upper plug 70 and consequently brought into a tight engagement therewith, with the result that the air will be pushed out of the empty space 21 and released through the grooves 72.
When the pressure inside the space 21 and the injection pressure of the material are equal, the core shaft 1 and the caps 50 and 60 descend under their own weight. Consequently, the tapered surface 51 of the cap 50 fitted on the lower part of the core shaft 1 is pressed against the tapered surface 41 of the lower plug 40 and brought into tight engagement therewith as illustrated in Fig. 4, so that the two tapered surfaces will jointly function as a check valve. As a result, the pressure inside of the space 21 is retained intact until the liquid rubber or plastics material is set. After the material is set, the core shaft 1 is pulled out of the cylindrical mold 30 to produce the rubber or plastics-coated roller of the present invention. The rubber or plastics layer 2 of the roller so produced has a uniform wall-thickness and is found to contain absolutely no discernible pinhole or air bubbles. When the air release grooves are formed in the tapered surface 71 of the upper plug 70, the burrs partly formed on the end faces of the core shaft are in the shape of cords and therefore can be easily ripped off. Thus, the end faces do not require any special secondary treatment.
Fig. 5 illustrates a roller producing apparatus of advantageous embodiment of this invention. In the Figure, the reference numeral 111 denotes a storage tank having an open mouth 111 a formed in the upper part thereof and containing therein a liquid molding material 8 such as liquid rubber or plastics material. Inside this storage tank 111 is held upright a hollow cylindrical member 115, which is attached to a support frame 114 vertically movable by an elevating device 113, such as, for example, a hydraulic cylinder or an air cylinder. To the lower part of this hollow cylindrical member 115, a valve member 116 is detachably fastened. This valve member 116 comprises a plug member 116a possessing a tapered surface and having a material inlet hold open at the centre thereof, a spherical member 116b adjoining the tapered surface of the plug member 116a, and a pin 116c for preventing the spherical member 116b from slipping. The spherical member 116b assumes an open state when the liquid molding material flows into the hollow cylindrical member 115. When the pressure in the hollow cylindrical member 115 is increased, the spherical member 116b is pressed against the tapered surface of the plug member 116a and is thus caused to assume a closed state.
Into the hollow cylindrical member 115 is inserted a hollow piston member 119, which is supported by a support frame 118 attached to the upper part of the support frame 114 vertically movable by an elevating device 117 such as, for example, a hydraulic cylinder or an air cylinder. To the lower part of the hollow piston member 119 is detachably fastened a valve member 120, which is composed of a plug member 120a, a spherical member 120b, and a pin 120c similar to the valve member 116 mentioned above. A metal mold 122 as described above is fastened through an injection tube 121, to the upper part of the hollow piston member 119.
In the roller producing apparatus constructed as described above, the roller is produced as follows.
First, by evacuating the interior of the hollow piston member 119 and the interior of the hollow cylindrical member 115, the liquid molding material in the storage tank 111 is caused to fill the interior of the hollow cylindrical member 115 and the interior of the hollow piston member 119. Then, the metal die 122 is fastened to the hollow piston member 119, through the injection tube 121. Subsequently, the hollow piston member 119 is lowered by elevating device 117 of the support frame 118. As a result, the liquid molding material 8 which has filled the interior of the hollow piston member 119 is caused to flow into the metal die 122. After the hollow piston member has descended to the lowermost part of the hollow cylindrical member 115, the hollow piston member 119 is elevated by the elevating device 117 of the support 118. Consequently, the liquid molding material held in the storage tank 111 is allowed to flow into the hollow cylindrical member 115. When the vertical reciprocation of the hollow piston member 119 is repeated, the metal die 122 is filled with the prescribed amount of the liquid molding material 8 and the pressure inside of the metal die 122 and the pressure for upward push given to the hollow piston member 119 are equlibrated. Consequently, the interior of the metal die 122 is pressed and the liquid molding material 8 is allowed to set to give rise to a roller.
In the present working example, the liquid molding material 8 can be consistently fed into the hollow cylinder member 115 because the hollow cylindrical member 115 provided with the valve member 116 is disposed inside the storage tank 111, the vertically movable hollow piston member 119 is inserted into the hollow cylindrical member 115, and the metal die 122 is fastened to the upper part of the hollow piston member 119, through the injection tube 121. Further, the cleaning of the set material can be easily carried out because the apparatus itself has simple construction. Thus, the roller can be manufactured with high efficiency.